There has been a continuing need for improving the oil/water ratio during hydrocarbon production. One way to improve hydrocarbon production is by using chemical gel systems to resist the flow of injected or natural aqueous drive fluid through high permeability channels and fractures, sometimes referred to in the art as “conformance control.” The general approach has been to inject a mixture of reagents, initially low in viscosity, into a zone of the formation that has high permeability. After a sufficient time to allow the mixture to be pumped into the subterranean formation or when exposed to the elevated temperature of the formation, the mixture of reagents then forms a gel to block the flow of water. Several mixtures of reagents have been used in this way.
U.S. Pat. No. 5,836,392 entitled “Oil And Gas Field Chemicals” and issued on Nov. 17, 1998, having named inventor Phillip Lance Urlwin-Smith, discloses a method for conformance control of a reservoir comprising injecting into a zone of the reservoir an aqueous solution of a copolymer comprising at least one ethylenically unsaturated polar monomer and at least one copolymerizable ethylenically unsaturated ester formed from a hydroxy compound of the formula ROH wherein R is a selected alkyl group, alkenyl group, cycloalkyl group, aryl group or such groups substituted with from 1 to 3 hydroxyl, ether or thio ether groups or a heterocyclic or selected heterocyclic alkylene group and at least one heteroatom selected from oxygen, nitrogen and sulfur and a selected alkenoic or aralkenoic carboxylic acid or sulfonic or phosphoric acid together with a crosslinking agent comprising a multivalent metal ion capable of crosslinking an acrylic acid polymer to form a viscous gel. The injected fluid is flowed through at least a portion of a high permeability region within said zone wherein it is heated to an elevated temperature whereupon crosslinking of the polymers occurs to form a substantially non-flowable gel within said high permeability region. The crosslinking of the injected fluid to form the non-flowable gel within the formation reduces the permeability of said region in said zone. See Abstract. U.S. Pat. No. 5,836,392 is incorporated herein by reference in its entirety.
U.S. Pat. No. 6,192,986 entitled “Blocking Composition For Use In Subterranean Formation,” issued Feb. 27, 2001, and having named inventors Phillip. Lance Urlwin-Smith, discloses a polymer composition for pumping downhole to gel in a subterranean formation comprising a water-soluble copolymer of (i) at least one non-acidic ethylenically unsaturated polar monomer and (ii) at least one copolymerisable ethylenically unsaturated ester; and an organic gelling agent therefore. Another water-based gel system for conformance control is based on a polyethyleneimine (PEI) crosslinker and a copolymer of acrylamide and t-butyl acrylate. See Abstract. U.S. Pat. No. 6,192,986 is incorporated herein by reference in its entirety.
While the use of aqueous polymer fluids to reduce undesired water production has achieved varying degrees of success, these fluids are undesirable in that they either have short gel times or low gel stabilities at high temperatures, high toxicity, and/or bio-accumulate in the environment. Short gel times for aqueous polymer fluids do not allow for adequate placement time in the zone of interest because they prematurely gel due to the elevated temperatures in the well bore and in the formation. Hence, these aqueous polymer fluids require pre-cooling the formation by injecting copious amounts of aqueous fluids prior to injecting gelling composition.